Conventional ultrasound imaging systems typically include a hand-held scan head coupled by a cable to a large rack-mounted console processing and display unit. The scan head typically includes an array of ultrasonic transducers which transmit ultrasonic energy into a region being imaged and receive reflected ultrasonic energy returning from the region. The transducers convert the received ultrasonic energy into low-level electrical signals which are transferred over the cable to the processing unit. The processing unit applies appropriate beam forming techniques such as dynamic focusing to combine the signals from the transducers to generate an image of the region of interest.
Typical conventional ultrasound systems include transducer arrays having a plurality, for example 128, of ultrasonic transducers. Each transducer is associated with its own processing circuitry located in the console processing unit. The processing circuitry typically includes driver circuits which, in the transmit mode, send precisely timed drive pulses to the transducer to initiate transmission of the ultrasonic signal. These transmit timing pulses are forwarded from the console processing unit along the cable to the scan head. In the receive mode, beam forming circuits of the processing circuitry introduce the appropriate delay into each low-level electrical signal from the transducers to dynamically focus the signals such that an accurate image can subsequently be generated.
For phased array or curved linear scan heads, the ultrasound signal is received and digitized in its natural polar (r,.theta.) form. For display, this representation is inconvenient, so it is converted into a rectangular (x,y) representation for further processing. The rectangular representation is digitally corrected for the dynamic range and brightness of various displays and hard-copy devices. The data can also be stored and retrieved for redisplay. In making the conversion between polar and rectangular coordinates, the (x,y) values must be computed from the (r,.theta.) values because the points on the (r,.theta.) array and the rectangular (x,y) grid are not coincident.
In prior scan conversion systems, each point on the (x,y) grid is visited and its value is computed from the values of the two nearest .theta. values by linear interpolation or the four nearest neighbors on the (r,.theta.) array by bi-linear interpolation. This is accomplished by use of a finite state machine to generate the (x,y) traversal pattern, a bidirectional shift register to hold the (r,.theta.) data samples in a large number of digital logic and memory units to control the process and ensure that the correct asynchronously received samples of (r,.theta.) data arrive for interpolation at the right time for each (x,y) point. This prior implementation can be both inflexible and unnecessarily complex. Despite the extensive control hardware, only a single path through the (x,y) array is possible.